Mammography has long been used to screen for breast cancer and other abnormalities. Traditionally, mammograms were formed on X-ray film, but more recently flat panel digital imagers have been introduced that acquire a mammogram in digital form and thereby facilitate analysis and storage. Further, X-ray tomosynthesis of the breast has been proposed recently, as discussed in the earlier-filed applications identified above, and clinical testing has been carried out. The assignee of this patent specification, Hologic, Inc., has demonstrated at trade shows in this country a fused, multimode mammography/tomosynthesis system that takes either or both types of images, and either while the breast remains immobilized or in different compressions of the breast.
Tomosynthesis as used in the systems and methods disclosed in this patent specification typically involves acquiring a plurality of tomosynthesis projection images Tp at respective angles relative to the breast, and reconstructing therefrom a plurality of tomosynthesis reconstructed images Tr representative of breast slices. Proper display techniques are desirable to make the presentation of Tp and/or Tr images more effective and efficient for review by health professionals. When tomosynthesis projection images Tp are acquired along with conventional 2D mammograms Mp, improved display methods are desirable that facilitate the display of both types of images. Effective display approaches also are desirable when tomosynthesis images Tp or Tr that are acquired at one time need to be compared to mammograms Mp or to tomosynthesis images Tp or Tr acquired at a different time. Another display issue relates to Computer Aided Detection (CAD) methods that use computer analysis of images to identify locations and possibly other characteristics of suspected abnormalities. CAD marks currently are placed on mammogram images Mp, but it may be useful to place them at the appropriate location on Tr or Tp images. Conversely, it may be desirable to obtain CAD marks by processing Tp and/or Tr images, and place them at appropriate locations on Mp images. Here the notation Mp refers to a conventional mammogram, which is a two-dimensional projection image of a breast; the term Mp encompasses both a digital image as acquired by a flat panel detector or another imaging device and the image after conventional processing to prepare it for display to a health professional or for storage, e.g. in the PACS system of a hospital or another institution. Tp refers to an image that is similarly two-dimensional but is taken at a respective tomosynthesis angle between the breast and the origin of the imaging X-rays (typically the focal spot of an X-ray tube), and also encompasses the image as acquired as well as the image after being processed for display or for some other use. Tr refers to an image that is reconstructed from images Tp, for example in the manner described in said earlier-filed patent applications, and represents a slice of the breast as it would appear in a projection X-ray image of that slice, and also encompasses information sufficient to describe such a slice image. The images Mp, Tp and Tr typically are in digital form before being displayed, and are defined by information identifying properties of each pixel in a two-dimensional array of pixels. The pixel values typically relate to respective measured or estimated or computed responses to X-rays of corresponding volumes in the breast.
Yet another issue concerns the large storage requirements of tomosynthesis images Tp and/or Tr. Because the reconstructed datasets for Tr images are large, it may be better in some circumstances to store unreconstructed projections Tp, which require less storage. Transmission times to the storage device, and from the storage device to the display workstation, can thus be reduced. The Tp images in this case can be reconstructed to Tr images just prior to viewing. Further, it may be desirable that images viewed on a workstation are the same or at least comparable to images viewed on a different workstation, or the same or at least comparable to images previously viewed of the same dataset, even if the software and/or hardware of the acquisition or workstation, or acquisition system, has changed.
Yet another issue concerns the processing time required to reconstruct tomosynthesis images Tr. Because of relatively long reconstruction times, one possible approach is to perform reconstructions at an acquisition console, and send the already-reconstructed images to display workstations. This can allow a greater reading throughput if there are several acquisition systems that are all pushing images to one or more display workstations. The system can be designed so that it can handle M acquisition consoles sending their images to all N display workstations.
In one non-limiting example disclosed in this patent specification, acquisition and display of x-ray images starts with acquiring x-ray mammography image data representative of projection mammography images Mp of patients' breasts and x-ray tomosynthesis image data representative of projection images Tp taken at different angles of at least a source of imaging x-rays relative to the patients' breasts (e.g., different angles of the focal spot in an X-ray tube relative an immobilized breast). This acquisition can be performed by a single unit, using a single X-ray tube and a single flat panel digital imager or some other imaging device, configured to selectively acquire one or both of the mammography and tomosynthesis image data, in the same compression of a patient's breast or in different compressions. The disclosed system and method use at least a subset of the acquired Tp images to form reconstructed tomosynthesis images Tr representative of slices of the breasts that have selected orientations and thicknesses. The system and method display at least a selected subcombination of the Mp, Tr and Tp images, preferably for concurrent viewing and preferably while showing, at or near the displayed images, respective labeling symbols identifying them as Mp, Tr or Tp images.
The method and system can further generate or otherwise obtain computer aided detection (CAD) marks for suspected abnormalities in said Mp images, and can display said marks at corresponding locations on Tr images associated, e.g. by orientation, with respective Mp images. In addition to location information, the CAD marks can provide information regarding, for example, the type of suspected abnormality and/or a confidence level that the marks points to an actual abnormality. CAD marks that are initially generated from or are otherwise related to some of the Tr, Tp or Mp images can be displayed at images from which they were not generated or with which they were not initially associated, at corresponding or at least related locations. Tp images can be stored together with version information indicative of at least one of an acquisition configuration used to acquire them and a reconstruction configuration used to reconstruct Tr images from said Tp images, to thereby enable later reconstruction of Tr images that match those reconstructed originally. Alternatively, or in addition, Tp images can be stored together with version information related to when they were acquired and can be later reconstructed into Tr images using a reconstruction configuration that matches the version information. A reconstruction configuration can be provided that has at least two different versions of reconstruction software, so that Tr images can be reconstructed using a version of the reconstruction software that matches the version information of the Tp images or earlier Tr images. Tr images can be reconstructed from only a subset of the acquired Tp images, which in an extreme case means reconstruction from a single Tp image to yield an equivalent of the Tp image. Tr images representative of at least two breast slices that differ in thickness can be formed, for example using MIP (Maximum Intensity Projection) methods or a summing method that may or may not use different weighting of the summed pixel data. The display can be toggled between Tr images representative of breast slices having different thicknesses, wherein the slices may or may not overlap in space. Through computer-processing, the volume of a lesion can be computed and displayed from information contained in the Mp, Tr and/or Tp images. The display can show concurrently Tr images reconstructed from a current acquisition of Tp images and at least one Mp image obtained from a previous acquisition involving a different breast compression. The concurrent display can be on the same or different monitors, and can include at least Mp and Tr images, or at least Mp and Tp, images, or at least Tr and Tp images, or all three types of images, and can instead or additionally include 3D images formed from some or all of the acquired X-ray data, image data and/or from Mp, Tr and/or Tp images. Information indicative of status of loading Tr images for display can be shown as a part of the display. Different images can be displayed at different pixel sizes or fields of view or, alternatively, they can be selectively equalized by pixel size or field of view by selected types of interpolation or extrapolation, for example by up-converting to a smaller pixel size and thus a higher converted pixel count or by down-converting to a larger pixel size and thus a lower pixel count.
The concurrent display of Mp and Tr images can include displaying non-numeric indications of respective levels of displayed Tr images relative to Mp images, for example in the form of cross-lines on a bar related to displayed Mp images, wherein the height of the bar may relate to the thickness of the compressed breast, and/or non-numeric indications of respective thicknesses of breast slices represented by displayed Tr images, for example in the form of cross-bars of respective thickness on a bar related to Mp images. Instead, or in addition, numerical indications can be provided and displayed of the position of a slice image Tr relative to a breast imaged in an image Mp, and/or the thickness of the slice. Mp and Tr images can be shown overlaid on each other, and toggling can be allowed to switch between the image that is visible at the time. In addition, other image display effects can be provided, such as, without limitation, fade-in/fade-out and blending two or more images at respective weighting, as commonly used in post-production of television images and in known image processing software such as Photoshop from Adobe. Tr images can be displayed in cine mode, with selective control over the speed of changing from one image to another and/or the order of images for display relative to an order in which they were reconstructed. At least two sets of Tr images, e.g. Tr images reconstructed from different acquisitions of Tp images, can be shown concurrently and scrolled through in synchronism. A selection of initial or default display modes can be provided relating to the order, speed, slice thickness and/or other parameters of display of images, and user selection among those modes can be allowed. Information regarding image data acquisition, storage, reconstruction and/or other parameters can be selectively displayed. Tr images can be printed in an N×M format (where N and M are positive integers), and printing of images displayed concurrently on one or more monitors in WISIWIG format can be allowed. Compression of Mp, Tp and/or Tr images and/or of image data can be selectively carried out prior to storage. The compression can be lossless, or it can be lossy to a selected degree. Reconstruction of Tr images can be selectively carried out from compressed Tp images. Window/level controls can be provided for at least selected ones of the displayed images, and the controls can be set by the user, or automatically, to control the window width and/or the window level of only one, or only selected ones, or all of the displayed images. Image regions can be magnified for display, and the window/level controls automatically applied to the magnified regions. The Tr, or the Tp, or both the Tr and Tp images, can be stored in PACS storage. The Tp images can be acquired by using coarser binning in a direction of relative motion between the source of imaging x-rays and a breast during image acquisition. Alternatively, such binning can be done after the Tp images are acquired, to thereby reduce storage and further processing requirements. The Mp and Tp images that are concurrently displayed can be acquired from the same breast of a patient while the breast remains immobilized under compression that can remain the same or change between the acquisition of Mp images and Tp images. Alternatively, the Mp and Tp images can come from different acquisitions at different times or different breast compressions. Image data for Tp images acquired at two or more acquisition units can be supplied to and reconstructed into Tr images at a single reconstruction unit, from which one or more data display units can acquire Tr images for display, or image data for Tp images can be stored as such and only reconstructed into Tr images immediately prior to display thereof.
An additional or alternative display approach uses the Tp and/or Tr images in stereoscopic display. For example, when any two Tp images taken at different angles to the breast are displayed concurrently and viewed such that each is seen by a different eye of the observer, depth information is visualized. Similarly, when any two Tr images are reconstructed such that their image planes are at an angle to each other, depth information can also be perceived.